Voltage regulators



'Dec. 6, 1966 w. SINCLAIR 3,290,583

VOLTAGE REGULATORS Filed Jan. 24, 1963 United States Patent 3,290,583VOLTAGE REGULATORS Walter Sinclair, Hemel Hempstead, England, assignorto Rotax Limited, London, England Filed Jan. 24, 1963, Ser. No. 253,730Claims priority, application Great Britain, Feb. 6, 1962, 4,463/ 62 6Claims. (Cl. 3239) This invention relates to voltage regulators of thekind in which a DC. supply circuit is broken intermittently for periodssufiicient to maintain the average voltage at a desired value.

A voltage regulator according to the invention comprises in combinationa pair of input terminals for connection to the supply to be regulated,a pair of output terminals for connection to a load, a transistor havingits emitter and collector connected between one of the input terminalsand one of the output terminals, a square wave oscillator operable bysaid supply to produce an output consisting of successive positive andnegative half-cycles, a pair of switching circuits through which theoutput from the oscillator is applied to the base of the transistor sothat at the commencement of each half-cycle of the oscillator thetransistor is rendered conductive, and means for interrupting the supplyto the base of the transistor at a time in each half-cycle which isvariable in accordance with the supply voltage across the outputterminals.

The accompanying drawing is a circuit diagram illustrating one exampleof the invention.

Referring to the drawing, there are provided a pair of input terminals1, 2 which are connected to a DC. source 3, and a pair of outputterminals 4, 5 between which a load 6 is connected. The terminals 2, 5are interconnected, whilst the terminal 1 is connected to the emitter ofa transistor 7 having its collector connected to the terminal 4.

The base of the transistor 7 is connected to one end of the secondarywinding 8 of a transformer 9 through a diode 10 in series with aresistor 11, and is further connected to the other end of the winding 8through a diode 12 in series with a resistor 13. The centre point of thewinding 8 is connected to the terminal 1. Opposite ends of the winding 8are connected to the anodes of controlled 'rectifiers 14, 15respectively, the cathodes of these controlled rectifiers beinginterconnected, and the gates of the controlled rectifiers beingconnected to their respective cathodes through diodes 16, 17. Moreover,the cathodes of the controlled rectifiers 14, 15 are connected through aresistor 80 to the base of the transistor 7.

The transformer 9 further includes a primary winding 18 and controlwindings 19, 20. The windings 19, 26 each have one end connected throughresistors 23, 24 respectively to the bases of transistors 21, 22.Moreover, the other end of the windings 19, are connected through adiode 25 to the emitter of the transistors 21, 22. The collectors of thetransistors 21, 22 are connected to opposite ends of the winding 18,whilst said other end of the winding 19 is connected to the mid-point ofthe winding 18 through resistors 26, 27 in series. The pointintermediate the resistors 26, 27 is connected to the terminal 2.

The terminals 4, 5 are bridged by two parallel circuits, one of whichcontains a diode 28, and the other of which contains a resistor 29 inseries with a resistor 30, the resistor 30 being bridged by a capacitor31. A variable point on the resistor 31 is connected through a resistor32 to the base of a transistor 33, the emitter of which is connected tothe terminal 2 through a Zener diode 34 bridged by a capacitor 35. Thebase and collector of the transistor 33 are bridged by a capacitor 36and a resistor 37 in series, whilst the emitter of the transistor 33 isconnected through a resistor 38 to the terminal 1.

3,290,583 Patented Dec. 6, 1966 The collector of the transistor 33 isfurther connected through a resistor 39 to the base of a transistor 40,the collector and emitter of which are bridged by a variable resistor 42the emitter of which is connected to the terminal 1 through a resistor41, and the base of which is connected to the terminal 1 through aresistor 43 in series with the resistor 41. The collector of thetransistor 40 is connected to the terminal 2 through a resistor 44 inseries with a capacitor 45, a point intermediate the resistor 44 andcapacitor 45 being connected to the emitter of a unijunction transistor46.

The unijunction transistor 46 has its primary and secondary baseterminals bridged by a Zener diode 47 having a capacitor 48 in paralleltherewith. Moreover, the secondary base terminal of the unijunctiontransistor is connected to the terminal 2 through a resistor 49 which isbridged by the primary winding 50 of a transformer 51 having secondarywindings 52, 53. One end of the winding 52 is connected through aresistor 54 to the gate of the controlled rectifier 15 whilst its otherend is connected to the cathode of the controlled rectifier. One end ofthe winding 53 is connected through a resistor 55 to the gate of thecontrolled rectifier 14, whilst its other end is connected to thecathode of the controlled rectifier 14.

The capacitor 45 is bridged by the collector and emitter of a transistor56, the base of which is connected through a diode 57 to the terminal 2,and through a capacitor 58 and resistor 59 in series to the mid-point ofthe winding 18.

Between the collector of the transistor 7 and the terminal 4 is a seriestransductor which is connected to a full-wave bridge rectifier 61, andderives its AC. power from a transformer 63 having a primary winding 64and secondary winding 62.

Connected across the output of the full-wave bridge rectifier are threeparallel circuits containing respectively a resistor 65, a resistor 66,and a diode 67 and capacitor 68 in series. A point intermediate thediode 67 and capacitor 68 is connected through a diode 69 to the base ofthe transistor 33, and through a diode 7 0* to the emitter of thetransistor 33. The transformer 9 together with the components associatedwith its windings 18, 19, 20 form a square wave oscillator of knownform. On switching on current flows through the resistor 26 and Winding19 to switch on the transistor 21 and the resulting flow through thewinding 18 induces a feed-back signal to the base of the transistor 21to render it more conductive, whilst at the same time inducing a signalin the winding 20 to hold the transistor 22 off. However, when thetransistor 21 is fully conductive, there is no further feedback and thetransistor 22 becomes conductive, the transistor 21 being switched oil.For convenience, the output of the oscillator can be considered toconsist of odd and even half-cycles.

The emitter of the transistor 7 is of course connected to the midpointof winding 8 during both the odd and even half-cycles, and during theodd half-cycles the base of the transistor 7 is connected to said otherend of the winding 8 through a switching circuit constituted by thediode 12 and resistor 13. During the even half cycles, the base of thetransistor 7 is connected to said one end of the Winding 8 through afurther switching circuit constituted by the diode 10' and the resistor11. In either case, therefore, the transistor is rendered conductive topermit current flow to the load.

The output voltage is sensed by the resistance chain 29, 3t), andapplied to the base of the transistor 33, the emitter voltage of whichis held constant by the Zener diode 34. If, during a half-cycle, theoutput voltage rises above a predetermined value, the transistor 33conducts to render the transistor 40 conductive and permit charging ofthe capacitor 45. When the capacitor 45 has charged to a predeterminedlevel, the unijunction transistor 46 is rendered conductive and currentflows through the winding 50 of the transformer 51 to produce pulses inthe windings 52, 53. These pulses are applied to the gates of thecontrolled rectifiers 14, 15, and during the odd half-cycles of thesquare-Wave oscillator, the controlled rectifier 14 is renderedconductive whilst the controlled rectifier 15 is unaffected by thepulses. Similarly, during the even half-cycles the controlled rectifier15 is rendered conductive whilst the controlled rectifier 14 isunaffected. In either case, however, the transistor 7 is not only shortcircuited but actually has its base-emitter junction reversebiased bythe conducting controlled rectifier and so the transistor 7 is turnedoff and no current flows to the output terminal 4.

At the end of each half-cycle of the oscillator the voltage developedacross the resistor 27 serves to render the transistor 56 conductive andthereby discharge the capacitor 45. It will thus be appreciated, thatthe moment in each cycle when the transistor 46 conducts to apply pulsesto the controlled rectifiers depends upon the rate of charge of thecapacitor 45. This in turn depends on the degree of conduction of thetransistor 40, which depends upon the amount by which the output voltageexceeds the predetermined voltage. The circuit described also providesprotection against over-current faults. Thus, the output of the bridge61 is fed to the base of the transistor 33 and affects this transistorin the same way as the signal from the resistor 30. The circuit isadjusted so that the output from the bridge 61 does not render thetransistor 33 conductive unless the cur-rent flowing through the series.transductor 60 exceeds a predetermined value.

The oscillator and controlled rectifiers may be used to control morethan one transistor. For each additional transistor five extracomponents are required, these components being those corresponding toresistors 18, 11 and 13, and diodes and 12.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A DC. voltage regulator comprising in combination a pair of inputterminals for connection to the supply to be regulated, a pair of outputterminals for connection to a load, a transistor having its emitter andcollector connected between one of the input terminals and one of theoutput terminals, a square wave oscillator connected across said inputterminals so as to be operable by said supply, said square waveoscillator producing an output consisting of successive positive andnegative half-cycles, a pair of switching circuits through which theoutput from the oscillator is applied to the base of the transistor sothat at the commencement of each half-cycle of the oscillator thetransistor is rendered conductive, switch means in circuit with thebase-emitter junction of said transistor, said switch means whenconductive reverse biasing said base-emitter junction to turn saidtransistor oil, and control means for said switch means, said controlmeans being connected across said output terminals and controlling saidswitch means to turn ofl said transistor at a 'time in each half-cyclewhich is variable in accordance with the supply voltage across theoutput terminals.

2. A DC. voltage regulator comprising in combination a pair of inputterminals, a pair of output terminals, a D-.C. source connected betweenthe input terminals, a load connected between the output terminals, atransistor having its collector and emitter connected between one of theinput terminals and one of the output terminals, the other inputterminal being connected to the other output terminal, a square waveoscillator connected across said input terminals so as to be operable bysaid D.C. source, said oscillator producing an output consisting ofsuccessive positive and negative half-cycles, a pair of switchingcircuits through which the output from the oscillator is applied to thebase of the transistor so that at the commencement of each half-cycle ofthe oscillator the transistor is rendered conductive, a pair ofcontrolled rectifiers connected in circuit with the base-emitterjunction of said transistor, each of said controlled rectifiers servingwhen conductive to reverse bias said base-emitter junction to turn saidtransistor off, a pulse-producing circuit having connections to said output terminals, said pulse-producing circuit producing in each half-cyclean output pulse at a time in the half-cycle dependent on the outputvoltage across said output terminals, means connecting the output fromsaid pulse-producing circuit to the gates of the controlled rectifiers,and biasing means operable by said oscillator for biasing saidcontrolled rectifiers so that one of them is held non-conductive duringthe positive halfacycles of the oscillator output, and the othercontrolled rectifier is held non-conductive during the negativehalf-cycles of the oscillator output.

3. A DC. voltage regulator as claimed in claim 2 in which saidpulse-producing circuit includes a transformer having a pair ofsecondary windings connected to the gates of the controlled rectifiers,a unijunction transistor controlling current flow through the primarywinding of the transformer, a Zener diode maintaining a predeterminedvoltage across the base terminals of the unijunction transistor, acapacitor in circuit with the emitter of the unijunction transistor,means for discharging the capacitor at the end of each half-cycle of theoscillator output, and means operable when the output voltage exceeds apredetermined value for charging said capacitor at a rate dependent onthe difference between the output and predetermined voltages, so thatthe greater the output voltage the sooner in each half-cycle of theoscillator output the uni-junction transistor will conduct to switch onone of the controlled rectifiers.

4. A DC voltage regulator as claimed in claim 3 including a controltransistor for controlling the charging rate of said capacitor, meansfor maintaining the emitter voltage 'of said control transistorconstant, and means for applying a proportion of the voltage across saidoutput terminals to the base of said control transistor.

5. A DC voltage regulator as claimed in claim 4 including a seriestransductor connected in series with said transistor connected betweenthe input and output terminals, and a [full wave rectifier through whichthe transductor output is connected to the base of said controltransistor, where-by the charging rate of the capacitor is increasedwhen the current flowing to the output terminal exceeds a predeterminedvalue.

6. A DC. voltage regulator as claimed in claim 2 including means forinterrupting the supply to the base of the transistor when the currentflowing to the output terminals exceeds a predetermined value.

No references cited.

JOHN F. COUCH, Primary Examiner.

K. D. MOORE, Assistant Examiner,

2. A D.C. VOLTAGE REGULATOR COMPRISING IN COMBINATION A PAIR OF UNPUTTERMINALS, A PAIR OF OUTPUT TERMINALS, A D.C. SOURCE CONNECTED BETWEENTHE INPUT TERMINALS, A LOAD CONNECTED BETWEEN THE OUTPUT TERMINALS, ATRANSISTOR HAVING ITS COLLECTOR AND EMITTER CONNECTED BETWEEN ONE OF THEINPUT TERMINALS AND ONE OF THE OUTPUT TERMINALS, THE OTHER INPUTTERMINAL BEING CONNECTED TO THE OTHER OUTPUT TERMINAL, A SQUARE WAVEOSICLLATOR CONNECTED ACROSS SAID INPUT TERMINALS SO AS TO BE OPERABLE BYSAID D.C. SOURCE, SAID OSCILLATOR PRODUCING AN OUTPUT CONSISTING OFSUCCESSIVE POSITIVE AND NEGATIVE HALF-CYCLES, A PAIR OF SWITCHINGCIRCUITS THROUGH WHICH THE OUTPUT FROM THE OSCILLATOR IS APPLIED TO THEBASE OF THE TRANSISTOR SO THAT AT THE COMMENCEMENT OF EACH HALF-CYCLE OFTHE OSCILLATOR THE TRANSISTOR IS RENDERED CONDUCTIVE, A PAIR OFCONTROLLED RECTIFIERS CONNECTED IN CIRCUIT WITH THE BASE-EMITTERJUNCTION OF SAID TRANSISTOR, EACH OF SAID CONTROLLED RECTIFIERS SERVINGWHEN CONDUCTIVE TO REVERSE BIAS SAID BASE-EMITTER JUNCTION TO TURN SAIDTRANSISTOR OFF, A PULSE-PRODUCING CIRCUIT HAVING CONNECTIONS TO SAIDOUTPUT TERMINALS, SAID PULSE-PRODUCING CIRCUIT PRODUCING IN HALF-CYCLEDEPENDENT ON OUTPUT PULSE AT A TIME IN THE HALF-CYCLE DEPENDENT ON THEOUTPUT VOLTAGE ACROSS SAID OUTPUT TERMINALS, MEANS CONNECTING THE OUTPUTFROM SAID PULSE-PRODUCING CIRCUIT TO THE GATES OF THE CONTROLLEDRECTIFIERS, AND BIASING MEANS OPERABLE BY SAID OSCILLATOR FOR BIASINGSAID CONTROLLED RECTIFIERS SO THAT ONE OF THEM IS HELD NON-CONDUCTIVEDURING THE POSITIVE HALF-CYCLE OF THE OSCILLATOR OUTPUT, AND THE OTHERCONTROLLED RECTIFIER IS HELD NON-CONDUCTIVE DURING THE NEGATIVEHALF-CYCLES OF THE OSCILLATOR OUTPUT.